Neutral beam probe spectroscopy for the measurement of local plasma density fluctuations

A neutral Li beam probing combined with a spectroscopic technique to measure local electron-density fluctuations is experimentally demonstrated in an ECR test plasma. The density fluctuations of up to 180 kHz are excited and controlled by applying periodic bursts of sinusoidal waves to a grid. The electron-density fluctuation levels thus obtained are found to agree well with those measured with a Langmuir probe. It is also suggested that this method can be applied to plasmas whose densities are in a wide range of 1010–1013 cm−3.